The present invention relates to a method for crushing mineral and organic materials; for example, a method of crushing a mineral material, whereby the mineral material is delivered to a crushing space of a bucket, in which space the mineral material is by crusher blades subjected to impacts decreasing its particle size, and mineral particles having a size meeting a predetermined cross-sectional measure are delivered to be discharged from the crushing space. Particularly, the present method is implementable by utilizing a mobile working machine.
The present invention also relates to an apparatus for crushing a mineral material for implementing said method of crushing mineral and organic materials.
It is, of course, previously known to carry out crushing by special devices called bucket crushers used in mobile working machines. Such devices include e.g. jaw crushers wherein normally in a working position an upper jaw is adapted to be mobile by means of either a hydraulic cylinder or a hydraulic motor. The mobile jaw of such a jaw crusher crushes the material loaded thereto against a stationary jaw. The material mainly consists of construction waste. In the jaw crusher, the entire material flow delivered thereto has to pass through the crusher in order to be discharged via an opening provided at a lower end of the pair of jaws. At the same time, the height of the opening at the lower end of the pair of jaws dictates the final maximum particle size of the crushed material being discharged from the jaw crusher, in which case the height of the opening is usually adapted to be adjustable in one way or another. Such a product is manufactured e.g. by a British company called Dig A Crusher Limited.
However, a problem with such a jaw crusher is a hopper provided by the jaw crusher's mobile jaw and stationary jaw therebetween. Being compelled to pass through this hopper, all material delivered to the jaw crusher will, of course, be gradually crushed into a desired particle size. Irrespective of the moving mechanism of the mobile jaw, in any case the jaw will only crush particles of material that happen to be appropriately located with respect to the pair of jaws. It is also typical of this device that larger particles of material to be crushed prevent smaller particles in the material flow from passing through. In addition, the structure of the mobile jaw of the jaw crusher has to be very robust, which means it is also quite heavy. Thus, owing to its large mass, the mobile jaw of the jaw crusher, when moving, causes a great inertial force which to a disadvantageous extent makes a boom of the excavator carrying the mobile jaw vibrate, thus shortening the service life of the boom. Owing to the large mass, the motion velocity of the jaw is also limited, thus requiring a good efficiency of the hydraulic arrangement controlling it. Also, since the jaw is capable of performing only one crush during each to-and-fro motion, the crushing capacity of the jaw crusher remains rather low. Also, the aforementioned phenomenon of small material particles being prevented from passing through adds to decreasing the crushing power of such a device.
On the other hand, devices called screen crushers are known wherein the material is mainly screened but wherein crushing of earth clods or corresponding relatively soft or fragile pieces is also carried out by means of several rotating drums. In such screen crushers, blades are usually welded in between discs provided in a drum, in which case the blades move the material delivered to the device from between the discs to a screen heap. Such devices are manufactured e.g. by a Finnish company called ALLU Finland Oy. Such devices are also described e.g. in patent specification JP 2001293385 or utility model specification DE 202 05 892.
In such devices, the material becomes crushed only if it is sufficiently fragile or soft. These devices are based on so-called gravitational feed, i.e. the material is crushed only if a stroke of a blade suffices to break the material. On the other hand, a problem arising with such a screen crusher is also the excess density of the material delivered to the bucket, in which case the material tends to get hung up inside the bucket. This is because the drums, including their blades, of the device only work their own space in to the material, whereby the rest of the material inside the bucket is no longer allowed to flow down to the drums. In order to prevent the material from becoming hung up, the bucket of the screen crusher is usually made quite shallow. This makes it possible to ensure that the material flow to the drums is better and more uniform. However, the structure of the known screen crushers is not designed for crushing hard mineral pieces but all material that after a screening cycle is larger than an interspace between discs is emptied in to a separate waste heap. Consequently, the device causes considerable noise disturbing the environment when a material abundant in rocks is screened. The screen crusher is incapable of crushing rocks but they remain inside the bucket, bouncing around. When the structure of the device is low, the noise caused by the screen crusher spreads out to the environment of the device with no difficulty.